The present invention is directed to a scraper blade for use in a conveyor belt cleaner mechanism for the removal of adherent material from a conveyor belt, and in particular, to a scraper blade which includes a structure adapted to control or eliminate the amplitude of vibration of the scraper blade during use when the face of the blade is located at a right angle or an obtuse cleaning angle relative to the conveyor belt.
Scraper blades are used in conveyor belt cleaning mechanisms to remove material which adheres to the belt surface after the material has passed the material discharge point of the conveyor. The cleaning angle of a scraper blade, which is the angle between the surface of the conveyor belt and the face of the scraper blade which faces the oncoming belt, may be an acute angle of less than 90.degree., a right angle of 90.degree., or an obtuse angle of greater than 90.degree.. As used hereinafter, "obtuse angle" shall include a right angle of 90.degree..
Scraper blades that operate at an acute cleaning angle tend to trap material between the belt surface and the scraper blade as the direction of movement of the adherent material must change by greater than 90.degree. during removal. This action is often referred to as "scraping". A scraper blade operating at an acute cleaning angle may also separate from the belt surface due to an accumulation of trapped material between the blade and the conveyor belt, a condition known as "planing."
A scraper blade that operates at an obtuse cleaning angle is more efficient in removing adherent material from the belt as adherent material does not become trapped between the blade and the belt and as adherent material can be removed with a smaller change in the direction of travel of the adherent material than with a scraper blade having an acute cleaning angle. This action is often referred to as "peeling".
While an obtuse cleaning angle is preferable over an acute cleaning angle, and a resiliently mounted blade is preferable to a rigidly mounted blade, resiliently mounted scraper blades having an obtuse cleaning angle are subject to destructive and cleaning efficiency reducing vibration at the scraping edge of the scraper blade. When a scraper blade is engaged against the belt surface, a rotational moment is created in the scraper blade by the drag of the belt over the edge of the scraper blade. When pressed against a conveyor belt, with a predetermined force to generate a predetermined cleaning pressure, a resiliently mounted scraper blade having an acute cleaning angle will rotate in a direction away from the belt surface, thus reducing the drag force created by the belt. This results in a comparatively small rotation and consequently only a small change in orientation from the scraper blade's natural orientation, thus producing a relatively stable and constant relationship between the blade and the belt surface with little or no resulting scraper blade vibration.
A resiliently mounted scraper blade having an obtuse cleaning angle, and applied against the belt with the same predetermined cleaning pressure will rotate in a direction toward the belt surface, causing a reaction in the blade supporting mechanism which moves in a direction away from the belt surface thereby reducing the drag force, which immediately causes the resiliently mounted blade to snap back to its natural orientation allowing the blade support mechanism to rotate towards the belt surface and resume the predetermined cleaning pressure which causes the same cycle of action and reaction to begin all over again. This unstable fluctuating relationship between the blade and the belt surface is seen as vibration of the scraping edge of the scraper blade relative to the belt surface, which is undesirable.
Scraper blades having an obtuse cleaning angle have previously been used as shown in U.S. Pat. No. 4,787,500. Ribs and other devices have been used to strengthen the base of a scraper blade, but such reinforcements control vibration of the scraping edge by increasing rigidity, thus reducing resiliency, and thereby increasing the risk of damage to the conveyor belt and the belt cleaning device.